Abstract In this study, a collision risk model was developed, based on gas model theory and Pedersen's collision and grounding mechanics. Busan north port was chosen as the area of assessment and, was divided into equal cells. Geometrical collision risk, both ship-ship and ship-structure, within each cell was analyzed following a probabilistic quantification. Moreover, bathymetry data of the port waters were analyzed to assess grounding risks. Results were plotted on Google Earth TM to identify the highest risk point and region within the area of assessment to aid safe maneuvering of vessels. Introduction With the recent trends and advancements in maritime world, emergence of new ships is inescapable and consequently, maritime traffic density has continued to expand. Increased number of ships, as well as bigger ships in narrow passages attribute to higher volumes of traffic in already congested waterways and particularly, in port areas. This, in turn, makes ship maneuvering more difficult and complicated. Moreover, higher maritime traffic can increase the risk of collision accidents with unfavorable consequences. Although some major technological advancements such as ECDIS (Electronic Chart Display and Information System), ARPA (Automatic Radar Plotting Aids), GNSS (Global Navigation Satellite System) and GMDSS (Global Maritime Distress & Safety System) are successfully integrated with navigation, port and harbor areas are still more susceptible to collision accidents. Thus, evaluating the risk of collision has become an integral part in maneuvering supporting systems to improve safety in navigation by decreasing the risk of collision. Collision risk in navigation is often misread due to the rarity of disastrous, individual accidents. Ylitalo (2010) discovered that the probability of an accident in a particular area would not be zero, although there is less or no records of previous incidents. Even though the probability of a direct ship-ship collision is very small, a minor incident can have unfavorable consequences, which can lead to loss of property as well as life at sea. Therefore, all risks in navigation have to be taken seriously. Identifying the risk areas, therefore, is vital to minimize and to avoid accidents. Once the risk areas are clearly identified, measures such as emergency planning can be taken for safe maneuvering of ships.

ABSTRACT With the increase of human activities at sea, it is inevitable that anchors drop into the water due to operating errors, which may lead to failure of pipelines and cause economic damage and environmental pollution. Previous methods of related analysis are mostly based on the DNV-RP-F107 recommended method (hereinafter referred as DNV method). DNV method hardly considers the variation of anchor's size and weight. And it is insensitive to the pipeline geometry and material properties. Based on reliability theory, DNV method is improved to calculate failure probability under the consideration of the above relevant factors. The efficiency of the proposed method is verified by a practical case. Besides, analysis of the influence of various factors on pipeline failure probability is completed in this paper, including anchor weight, size, pipeline geometry and material properties, the distance from the anchor drop point. Meanwhile, considering the variability, the sensitivities of variables to the failure probability are discussed. Study results indicate that the failure probability calculated by DNV method is underestimated in some situations, which can probably cause a loss for pipeline projects. Whereas the proposed method is able to consider much more influences and leads to reasonable results consistent with the actual situation. INTRODUCTION Submarine pipeline is seen as the ‘lifeline’ for offshore oil and gas industry. Pipeline safety is one of the most important problems for engineering practice. Recently, anchors dropping into the sea becomes more frequent due to the increasing human activities at sea. The dropped anchors are likely to impact on pipelines and lead to pipeline failures, which can cause economic damage and environmental pollution. In order to reduce the risk and provide safe design, considerable research efforts have been devoted to risk assessment and reliability analysis of pipelines. In general, methods of the relevant research mainly consist of two categories: one is qualitative analysis, which can study the main influence factors on pipeline failures. Among them, fault tree analysis (FTA) is the most popular methodology and has been extensively applied to pipeline failure analysis. (Wang et al., 2007; Dong et al., 2005; Lavasani et al., 2011). The other one is quantitative analysis, which can determine pipeline failure probability and provide reliable reference for safe design. Katteland et al. (1995) developed a model for risk calculation, and applied it to evaluate the risk of all the installations in the North Sea. Det Norske Veritas (2010) proposed a ubiquitously used method for pipeline risk assessment and failure probability calculation (DNV method). Based on statistics of crane accidents, Det Norske Veritas (2013) also gave the falling probability for typical loads and various objects, which provided abundant references for pipeline risk assessment. On the basic of the above research, Liu et al. (2005) proposed a model to calculate the probability of pipeline being impacted under various anchorage conditions. Ding et al. (2010) modified DNV method and made a risk assessment of pipelines due to third-party activities. Yan et al. (2014) proposed a procedure to estimate the pipeline failure probability caused by anchoring activities. Up to now, to the best of the author's knowledge, quantitative analysis methods are mainly based on DNV method. In some situations, this method is hardly to consider the effect of anchor size and weight on pipeline failure probability. What's more, it is insensitive to the effect of pipeline geometry and material properties, which is not consistent with practice and may cause errors. In order to give an insight into those effects, a method based on reliability theory to calculate pipeline failure probability is proposed.

Abstract This paper introduces the Shenzhen-Hong Kong submarine pipeline of West to East Gas Pipeline II Project. In specific environmental conditions and submarine pipeline's situation, we carried on the risk identification for pipeline suspending, drop anchor impacting and ship aground impacting. Consequence of failure is given out relating to pipeline suspending, drop anchor impacting and ship aground impacting. Pipeline risk probability is determined. Some specific measures are put forward to guard against submarine pipeline risks take place.

ABSTRACT: Ice conditions of the Arctic present the most significant hazard that offshore structures located there will encounter. In severe ice environments, ice loads influence size, stability, reliability and durability of engineering structures. In order to calculate ice load and effects from interacting ice features, it is necessary to determine statistical variability of the ice features, and develop probabilistic models of ice conditions. The purpose of this study is to develop the probabilistic model of the ice cover on the Raahe lighthouse in the Gulf of Bothnia, taking into account correlation and statistical dependence of essential factors of ice environment. For the probabilistic analysis and modeling the full-scale observation data of ice regime of an Oulu and Raahe lighthouses zone in the Gulf of Bothnia have been processed for winter seasons of 2005÷2009 years. The result of investigations is the probabilistic model of ice conditions at concrete foundation of Raahe lighthouse for various ice scenarios with a view on correlation and stochastic relationship between observed values of ice parameters. INTRODUCTION Ice investigations around lighthouses in the Gulf of Bothnia have been carried out for over 30 years by this time, and they have become more intensive in the last 5÷10 years with application of the up-to-date observation technologies and ice model tests. On this problem, dozens of the ice research programs have been realized and the significant amount of scientific studies and engineering reports from the key ice laboratories and centers has been published. On the basis of analysis of the available publications all the investigations can be divided conventionally as follows. 1. Regular full scale observations of hydrological, meteorological and ice regime of the sea area in the Gulf of Bothnia since 1979 till the present time with subsequent statistical data processing ( http://en.ilmatieteenlaitos.fi ).

ABSTRACT: Application of subsea technologies near shore or simultaneously with platforms far offshore on the Russian Arctic continental shelf with harsh ice conditions seems to be feasible or at least should be considered within the range of concepts due to possible good economical effect. Installation is one of the crucial marine operations related to the subsea technologies. Right forecast of the weather and wave conditions is the key issue in the planning of installation operation of subsea modules. Limitations of subsea installation related to waves have been shown in this work. Optimal time period for installation, probability of success per one season and mean time of installation have been determined on the basis of statistics accumulated in RMRs' directories. INTRODUCTION Subsea technologies on the Russian Arctic continental shelf with harsh ice conditions seem to be applicable or at least have to be considered within the range of concepts. Taking into account the significant progress achieved in offshore development with subsea technologies over last decades and increased reliability one may with high degree of certainty conclude that these systems are important and perspective for Russian shelf. This can also be confirmed by announced plans to use floating structures, which require elements of subsea development. At the same time there is a number of limiting factors enhancing the application of subsea technologies, such as long distances to the shore, ice gouge of seabed at the location of templates or pipelines, limited service and maintenance availability in ice infested waters, limited installation period. Installation is one of the crucial marine operations related to the subsea technologies, which can be executed during ice-free period lasting in some areas about 3-4 month. Therefore right weather forecast, forecast of wave conditions, assessment and determination of available and favorable installation period is a key issue.

ABSTRACT: The construction of the piers between Novosilsky Cape and Nazimova Peninsula decreased the width of the Strait of Bosphor-Vostochny by about 200 m. In winter 2009–2011, the formation of ice in the Straits of Bosphor-Vostochny took place more intensively than in years with hard ice cover. In January and February in the strait the water area from fast ice occupied much wider area than in cold winters past years. The destruction of the ice in March was the same as during the cold winters. Despite of low temperature, the intensive north wind causes lead formation in the northern part of the strait and makes the 9/10 ice in the southern part. Construction of the piers on the Novosilsky Cape and Nazimova Peninsula causes an increase in the width of the fast ice. This point requires clarification in the future. INTRODUCTION The width of the Strait of Bosphor Vostochny was reduced almost by one third because of the construction of the bridge to the Russky Island. Three-year study, the aim of which was to identify the possible consequences of the constriction of the Strait between Nazimova Peninsula and Novosilsky Cape showed that the change of the water exchange of the adjacent bays, as well as currents in the Strait was not too significant. The most severely narrowing of the Strait should have an impact on the ice, so the main aim of the research was to evaluate the changes of ice regime of the Straits of the Bosphor-East and adjacent bays: Ayaks, Paris. MATERIALS OF OBSERVATIONS The most severely narrowing of the Strait should have an impact on the ice, so the main aim of the research was to evaluate the changes of ice regime of the Bosphor-Vostochny Straits and adjacent bays: Ayaks, Paris.

ABSTRACT: Liquefied natural gas has the unique distinction of being the only flammable or hazardous material. Inspection effectiveness may be introduced into the probability of failure calculation by using Bayesian analysis or more directly by modifying the model for the independent variables, the distribution function and parameters, such as mean and coefficient of variation, changed based on the NDE method and coverage used during an inspection. Available failure data from the LNG industry are often statistically unreliable. Therefore, we need to improve more accurate information data. NDE reliability matrix is to apply optimization method of the NDE method. Environment parameters consist of inspector qualification and experience, test condition and inspection reliability parameters are composed of the inspection method and process method, such as UT, ET, RT and s/n ratio, signal processing method, etc. Finally, this paper purposes that the Reliability matrix is a powerful tool for risk assessment of not only the LNG industry but also in other industry. INTRODUCTION Liquefied natural gas is simply a convenient form of natural gas, a cryogenic liquid condensed in volume to make storage economically feasible. LNG is made at a liquefaction plant is restored to a gas at a regasification plant. In a liquefaction plant, there are several steps. The main steps, starting at the natural gas feed, include CO2 removal, dehydration and mercury removal, initial chilling, liquefaction, nitrogen rejection, finally, product LNG storage. LNG is a liquid mixture of light hydrocarbons. The main component is methane C1. And there have a other minority components such as nitrogen N2, ethane C2, propane C3, and traces of i-butane iC4, nbutane nC4, i-pentane iC5, n-pentane nC5(Mario and Rafael, 2010). The largest amount of LNG imported in 2005 was 58.6million tons to Japan, or 30% of the world trade in LNG.

ABSTRACT: The study is devoted to the problems of mathematical simulation of the physical process of interaction between the ice cover and the offshore engineering objects in terms of simulation and statistical methods. In the previous studies the authors made an attempt to describe a wider scope of possible scenarios of interaction which might cause an ice force extreme by value. The purpose of this study is to simulate effects of stable ice congestions which caused extreme ice loads on structures. INTRODUCTION When designing the structures intended for operation in the seas under severe ice conditions, it is necessary to consider a possible effect from the drifting ice features, such as level ice fields, layered or hummocky ice fields, individual hummocks, ridges of hummocks, grounded hummocks, icebergs, ice masses from icing-up, combinations thereof, etc. The offshore platforms are mostly affected by the drifting ice features (such as individual hummocks, ridges of hummocks, or giant level ice fields, as well), loads from which may be very high and become extreme for the platforms. The subject was considered urgent because the effect from the extreme ice features was one of the most difficult challenges to include during MIRP designing. From analysis of the worldwide investigations of ice effects on marine hydroengineering structures, as well as from the guidelines of the normative documents, it became clear that they had omitted a considerable portion of the calculated occurrences and kinds of effects which could occur in the open marine area. In addition, the analysis of references in the practice of ice load calculations showed that various researchers had considered basically the particular cases of the structure supports affected by any ice feature (such as the level/hummocky ice fields, grounded hummocks, icebergs, etc.) only.

ABSTRACT: Pile foundations are often subjected to horizontal loads. There are several deterministic techniques to analyze single piles under lateral loading. This paper implements a computationally inexpensive technique called Winkler approach to model the soil-pile system as vertical beam supported by a series of discrete springs. Beam and spring elements in structural analysis software, ABAQUS, are used in this study to predict response of a single pile under a horizontal load. It is known that soil properties, pile properties, and load systems dominate the performance of a pile and each has a different extent of uncertainty. It was found that the soil properties, lateral subgrade modulus of soil and ultimate soil resistance, in addition to the elastic modulus of pile material, and horizontal load were the most important parameters influencing the performance of piles. Random variation in these factors is studied using Monte Carlo simulation. It is shown that the likelihood of exceeding a specific level of maximum bending moment and pile head displacement for a given horizontal load can be used to construct failure probability curves to study the performance of piles due to the uncertainty in the aforementioned factors in the soilpile system. INTRODUCTION To support those structures, piles that are designed to carry horizontal loads are needed. Two aspects of interest which should be considered in designing a laterally loaded pile are the lateral pile head displacement and the maximum bending moment in the pile (Tandjiria et al, 2000). A pile is said to provide good performance if these two aspects are satisfied. The probability of failure of the pile can be defined as the likelihood of exceeding a specific level of pile head displacement and bending moment in the pile for a certain level of horizontal load applied at the pile head.

ABSTRACT: Group length which is defined as number of waves in a group, is an important rameter to evaluate groupiness. In this study, the maximum entrop distribution G , pa y () = α γ e x p (− β n ) n f G G G is applied to describe G , where α, β and γ can be determined by some reasonable constraints when n is given. For n =1, γ = 0, this distribution has the same form as the commonly used stribution derived by Longuet-Higgins (1984). Comparisons of both the maximum entropy distribution and the distribution of iggins (1984) with the laboratory wind-wave data show ives a better fit; it has the best agreement for n = 0.6. INTRODUCTION The grouping of sea waves plays a principle part in many coastal and ocean engineering problems, including low-frequency motions and force analyses of moored vessels, the stability of fixed or floating structures, as well as surf beats in the nearshore zone (Donelan et al., 1972; Goda, 1983; Tayfun, 1989). Besides, wave groups may cause exceptional damage to ships and offshore structures. Recent interest in the subject (Tayfun, 1990; Tayfun, 1994; Kit et al., 2000; Cho and Kim, 2005) has been stimulated by the probable effect of nonlinearity on the formation of a wave group. Wave envelope function is usually used for the description of group properties. Group, defined as number of waves between two successive up-crossings of crossing a given reference leve is an useful parameter to evaluate wave groupiness. In this paper, a new PDF is derived for the distribution of group length. The derivation is based only on the maximum entropy principle, without limitation of Gaussian process hypothesis.

ABSTRACT: This paper proposes a Bayesian-theory-based risk analysis method of coastal structure design criteria along Qingdao coasts of Yellow Sea. New method has some advantages over traditional method. This is because Bayesian theory continually involves new data and information in the process of prior probability and posterior probability exchanges and then improves the model of statistical prediction. The proposed method gives quantitative risk analysis of coastal structural stability. INTRODUCTION Traditional design method of coastal structures always bases on the calculation by design codes or experimental modeling tests. And sea environmental events are chosen as determinate combinations as input parameters. Different kinds of uncertainties of sea environments and sensitivity of structural responses to uncertainties of input parameters are not taken into consideration. However, uncertainties of wave heights, wave periods and water levels are remarkably important for coastal structures. The Bayesian theory based analysis method through the circle of prior probabilities--posterior probabilities involves different kinds of uncertainties and their corresponding correction during Bayesian analysis processes (Box and Tiao, 1973; Neter, Wasserman and Whitmore, 1988). Finally the most disadvantageous response for structural stability can be selected. SOME DEFINITIONS AND CONCEPTS OF BAYESIAN THEORY For following extreme sea environments induced wave forces and structural stability analysis, after first calibration circle of probability distribution models, for example, structural response induced by extreme wave height, the outcome state probability can be gotten. It is also called as prior probability because the sample information subsequently provides further information about the prevailing outcome state. Next, for the prior probability and the new data series (including different kinds of uncertainties) the posterior probability () i P M ( i ) P M i x () i i P M x can be obtained using Bayesian t y.

ABSTRACT: The theoretical analysis and the statement of problem of optimization of a spatial orientation of the subsea pipeline route taking into account the magnitude of its burial depth and a bottom configuration on the basis of probabilistic approach from the point of view of a mathematical reliability theory was carried out. Elements of a probabilistic simulation model of impact of drifting hummocks on a sea bottom and subsea pipelines are developed. Probabilistic characteristics of hummocks parameters and bottom configuration are obtained on a basis of specially developed algorithm and realized computer program with usage of the observation data of an ice regime parameters and geomorphology of sea bottom. The estimation of spatial orientation of the subsea pipeline route at Piltun-Astokhskoe oil-and-gas deposit located in the north-east area of Sakhalin offshore was made. INTRODUCTION Development of oil-and-gas resources offshore in the freezing seas is largely complicated because of the presence of an ice cover which influences special engineering structures (offshore platforms, artificial islands, the subsea line structures, drilling ships, engineering nets and communication lines, etc.). In this connection the problem of comprehensive study of ice impacts and development of calculation methods of ice loads on offshore structures remains actual more than one decade. As a rule, the pipeline transport is the most profitable mode of transport of oil and gas in development of sea deposits, including in the freezing seas (Mazurin, 1990). Trouble-free operation of the subsea pipeline significantly depends on the account of factors of environmental influence on projecting stages. The development of a pipeline network in the arctic regions leads to the growth of probability of a failure of pipelines by drifting hummocks and icebergs which are extreme ice formations and present the basic and greatest hazard to the subsea line structure.

ABSTRACT: Development of production platforms for promising Russian offshore areas in the Barents and Kara Seas and on Sakhalin island sets a challenge to overcome their extremely harsh environmental conditions. These are to manage ice in winter and heavy waves in other seasons (platforms and terminals in the Barents Sea) and, in addition, seismic events up to Force 9 (Sakhalin, the Sea of Okhotsk). Some experience has been gained in the design and installation of fixed ice-resistant platforms on the Russian offshore, for example, gravity-based «Vityaz» platform with a soil core («Sakhalin-II» field) deployed at a depth of 32 m. Gravitybased «Prirazlomnaya» platform for the Pechora Sea will be deployed at a depth of 19 m to operate under severe ice conditions. There is also a design of a piled platform developed by Exxon- Mobil for «Sakhalin-I» field. This paper presents an overview of general design principles for offshore ice-resistant platforms for the Russian offshore resulting from the design experience and comparison of Russian and Western codes and rules. INTRODUCTION This paper overviews design peculiarities of offshore ice-resistant fixed platforms designated for the Russian offshore (the Barents and Kara Seas and Sakhalin island). Unusually severe combination of environmental conditions in these seas is the major peculiarity of the Russian offshore. At the same time significant oil and gas reserves explored in these areas make the production reasonable and profitable. Design of these facilities calls for a new approach to standards, rules and codes and, first of all, for the development of estimation procedures and assignment of environmental loads. A difficult problem is to assign reasonable combinations of environmental loads, including those with a principally different recurrence period. Thus, a new approach to this problem is called for, an approach different from the proven western ones.

ABSTRACT: This paper presents a method of applying the probabilistic fracture mechanics techniques to the selection of excellent acceptance criteria for CTOD test, mainly focus1ng on the required fracture toughness and the number of test specimens. Several factors which are stochastic in nature are treated probabilistically. The required fracture toughness and the number of specimens to be tested in acceptance testing are considered in terms of its risk level and fracture probability vs. probability of acceptance respectively. INTRODUCTION The current acceptance criteria in general determine δ REQ using traditional deterministic fracture mechanics analysis. The deterministic analysis can not account for the reliability of δ REQ determined and in general selects the worst value which may be the unrealistic one. In dealing with problems such as these effectively a probabilistic approach is logical. The aim of this paper is to give a method of determining δ REQ and the appropriate number of specimens for CTOD test using probabilistic fracture mechan1cs techniques. The physical and mechan1cal concepts of fracture are primarily based on those of WES 2805. Reference structural components are the welded joints of marine structures subjected to sea wave induced stresses. such as ships and offshore structures. In carrying out the analysis stresses caused by sea waves, crack size and fracture toughness having a large scatter peculiarity for welds are taken as random variables which have their specific probabilistic distributions. The discussions are largely carried out based on numerical results. PROBABILISTIC DISTRIBUTION OF FRACTURE DRIVING PARAMETER δ Probabilistic Distribution of Applied Strain ε In WES 2805, ε is divided into three categories by its constituent elements namely ε caused by boundary force ε I. ε caused by welding residual stress ε 2. and t caused by welding joint profile responsible for localized strain concentration ε 3.

ABSTRACT: Presented is the numerical method algorithm of jacket type offshore stationary platforms dynamic calculation for the effect of two-dimensional random waves of finite, heights described by different spectra. Numerical research of single- and multilegged structures of different pliability with various diameters supports station and dynamic reactions under the action of random waves are cited. It is shown that structures dynamic reactions do not practically depend on wave spectrum type; probability of exceeding functions reactions mainly depending on wave load velocity and inertial components relation, structure pliability and its length along wave ray. INTRODUCTION Nowadays known are analytic methods of dynamic offshore structure calculation for random wave effect based on linear spectral wave theory and wave load linearization /1 2/. The limited use of these methods results in impossibility to define correctly distribution (probability of exceeding) functions of structures reactions. Well-defined theoretical solutions of offshore structures dynamic calculations for random wave of finite height are absent. This is explained by the difficulty of considering such factors as wave load non-linearity, wetted height variation of structure supports in time and space, structure length. To overcome these difficulties method of dynamic numerical calculation of deep water stationary jacket-type platforms under the action of two-dimensional random waves of finite height was developed. In wave load calculation the real three dimensional structure is replaced by a system of vertical supports of different diameters ("package of supports"), the wave load of which is equal to that of real structure. In dynamic calculation the structure design scheme is considered as linear damping system of single approximable leg rigidly fixed to the bottom. Distributed along the leg mass m is assumed constant and is equal to the sum of distributed mass of platform structure and added water mass.

ABSTRACT: This paper presents a fatigue testing method using a multi-notched test specimen for the purpose of estimating the distribution function of fatigue crack initiation life by a small number of, fatigue tests. Emphasis is placed on the effective use of the fatigue data provided by one test specimen to decrease the number of specimens required in the fatigue tests. The experimental results indicate that two or three multi-notched specimens are practically enough to determine the distribution function of crack initiation life. 1. INTRODUCTION Fatigue crack initiation life has a wide scatter and this makes the fatigue design of structural members difficult. In order to make -the fatigue life distribution clear, it is required to prepare a large number of specimens and repeat the fatigue tests under the same loading condition. Such fatigue tests usually take much time and cost. It will take still more time and cost to conduct the fatigue tests such as random fatigue tests or corrosion fatigue tests in long life range. The purpose of this study is to reduce the time(cost) required for the above fatigue tests by applying a multi-notched specimen. The multi-notched specimen is a specimen in which several tens of statistically identical notches are prepared. Heller et al.[l,2] analyzed the life distribution of multi-notched specimen with the aid of extreme value statistics. Itagaki et al.[3] improved the method of experiment and employed Bayes" theorem for the fatigue life analysis. The validity of this testing method is discussed through the fatigue tests using a multicircular- holed plate specimen. 2. FATIGUE TESTING METHOD AND STATISTICAL ANALYSIS METHOD 2.1 Fatigue Testing Method Consider a multi-notched specimen in which " M" number of statistically identical notches are prepared. For all the notches the time to fatigue crack initiation is assumed to follow a distribution function.

ABSTRACT: This paper is concerned with structural reliability of an offshore guyed tower for large storm events. Analysis is conducted in the light of the failure of an anchor pile of the guy line system. Two failure modes for the extreme and the cyclic loadings at an anchor pile are considered. Dynamic analysis of the tower to random waves is earned out in the frequency domain utilizing the stochastic linearizations of the nonlinear mooring force and the nonlinear drag force. The probability of failure due to the extreme anchor load is evaluated based on the results of the dynamic analysis using the first-excursion probability analysis. For the consideration of the degradation of pile capacity due to cyclic loadings, empirical fatigue curves for a driven pile in clay are used. The numerical results indicate that the failure probability due to the cyclic loadings can be fairly comparable to the risk due to the extreme loading, particularly for the case where the mean safety level of the pile strength is low and the uncertainties in the pile resistance are large. INTRODUCTION A reliability analysis of an offshore guyed tower for severe storm events is presented in this paper. More specifically, the reliability of an anchor pile of the guy line system is investigated. The guyed tower is one of the compliant structures recently developed for the deepsea oil production 1-3. Each line consists of a guyline catenary, a clump weight, an anchor line and an anchor pile. Under normal environmental conditions, the cable array acts as a hardening restraint. Under severe storm events, however, the clump weights are lifted from the seabed and the cable array acts as a softening restraint. This implies the geometric nonlinearity of the guyline system as in Fig. 2.